1. Field of the Invention
The present invention relates to a glass-ceramic composite material and a multilayered circuit substrate formed by using the glass-ceramic composite material. In particular, this invention relates to a glass-ceramic composite material for use in forming a multilayered circuit substrate capable of ensuring a low dielectric constant and a relatively high thermal expansion coefficient. In addition, this invention also relates to a multilayered circuit substrate formed by using such a glass-ceramic composite material.
2. Description of the Related Art
Since more and more electric devices have been made compact in recent years, many electronic parts for use in these electronic devices have also been required to be made compact in size. It is effective to employ circuit substrates capable of mounting electronic parts for use in these electronic devices in order to manufacture electronic devices which are compact in size. Further, a circuit substrate usually includes a laminated body formed by a plurality of electrically insulating layers. Accordingly, if a multilayered circuit substrate provided with conductive patterns is employed by making use of the laminated body, it is possible for the multilayered circuit substrate to contain in itself some electronic elements such as condensers and inductors, thereby further promoting the production of electronic devices which are all compact in size.
In the aforementioned multilayered circuit substrate, a ceramic is usually favorably employed as the material for forming the electrically insulating layers. However, in a case where the electrically insulating layers are formed by a ceramic material, a sintering process is usually carried out to form the laminated body including a plurality of ceramic layers laminated one above another. When such a sintering process is being carried out, the conductive pattern provided within the laminated body will also be sintered at the same time.
Electronic devices have not only been required to be made compact in size in recent years, but also to be capable of being used in a high frequency area.
In order for a multilayered circuit substrate to be suitably used in a high frequency area, it is necessary that the conductive pattern be made of a material having a low electric resistance. For this reason, an electrically conductive component contained in the conductive patterns has to be a metal having a low electric resistance, such as copper or silver.
A low resistance metal such as copper and silver also has a low melting point. Because of this, when the aforementioned sintering process is carried out and also sinters the conductive patterns containing such a low melting point metal, the ceramic material contained in the ceramic layers has to be sintered at a temperature of 1000° C. or lower in order to produce a desired laminated body including a plurality of ceramic layers.
A glass-ceramic composite material formed by adding a glass into a ceramic can be used as a material which can be sintered at a temperature of 1000° C. or lower.
If the multilayered circuit substrate is to be used in a high frequency area, as well as to mount conductive patterns with a high density, it is necessary for the electrically insulating layers to have a low dielectric constant. If the aforementioned glass-ceramic composite material is used as a material forming the electrically insulating layers, such a glass-ceramic composite material is required to have a relatively low dielectric constant. However, in a case where condensers are contained within the multilayered circuit substrate, the glass-ceramic composite layers providing such condensers are required to have a relatively high dielectric constant.
If a laminated body for use in forming the multilayered circuit substrate has a composite structure including glass-ceramic composite layers having a relative low dielectric constant and other glass-ceramic layers having a relative high dielectric constant, it will be possible to provide condensers having a large capacity but a small volume in portions having a relative high dielectric constant, and to provide a structure in other portions capable of satisfying the requirement concerning a high frequency as well as a requirement concerning a high density wiring.
However, in general, a glass-ceramic composite material having a high dielectric constant usually exhibits a high thermal expansion coefficient, while a glass-ceramic composite material having a low dielectric constant usually exhibits a low thermal expansion coefficient.
For this reason, the two kinds of glass-ceramic composite layers will exhibit mutually different thermal expansions and mutually different shrinking behaviors in the sintering process for producing a laminated body having a composite structure including two kinds of glass-ceramic composite layers having different dielectric constants. As a result, it is quite possible that defects such as crackings will occur in the obtained laminated body.
The aforementioned problems, however, can be solved if it is possible to produce a glass-ceramic composite material having a low dielectric constant but a relatively high thermal expansion coefficient.